Information signal representation using lapped transform

• US 9,536,530 B2
• Filed: 11/09/2012
• Issued: 01/03/2017
• Est. Priority Date: 02/14/2011
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Fotopoulou, Eleni, Schnell, Markus, Geiger, Ralf, Ravelli, Emmanuel
• Primary Examiner(s): Nguyen, Duc
• Assistant Examiner(s): Patel, Yogeshkumar
• Application Number:
  US13/672,935
• Publication Number:
  US 20130064383A1
• Time in Patent Office: 1,516 Days
• Field of Search: 704/500, 704/E19.02, 704/E19.011, 704/E19.005, 704/E19.015, 704/219, 704/E19.023, 704/E19.04, 704/E19.041, 704/204, 375/E7.226, 375/240, 375/240.03, 375/240.11, 381/123
• US Class Current: 1/1
• CPC Class Codes: G10K 11/16 Methods or devices for protecting against, or for damping, noise or other acoustic waves in general G10K11/36 takes precedence
• CPC Class Codes: G10L 19/00 Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis in musical instruments G10H
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm
• CPC Class Codes: G10L 19/012 Comfort noise or silence coding
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 19/025 Detection of transients or attacks for time/frequency resolution switching
• CPC Class Codes: G10L 19/03 Spectral prediction for preventing pre-echo; Temporary noise shaping [TNS], e.g. in MPEG2 or MPEG4
• CPC Class Codes: G10L 19/04 using predictive techniques
• CPC Class Codes: G10L 19/107 Sparse pulse excitation, e.g. by using algebraic codebook
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 19/18 Vocoders using multiple modes
• CPC Class Codes: G10L 19/22 Mode decision, i.e. based on audio signal content versus external parameters
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 21/0216 characterised by the method used for estimating noise
• CPC Class Codes: G10L 25/06 the extracted parameters being correlation coefficients
• CPC Class Codes: G10L 25/78 Detection of presence or absence of voice signals switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10

Abstract

An information signal reconstructor is configured to reconstruct, using aliasing cancellation, an information signal from a lapped transform representation of the information signal including, for each of consecutive, overlapping regions of the information signal, a transform of a windowed version of the respective region, wherein the information signal reconstructor is configured to reconstruct the information signal at a sample rate which changes at a border between a preceding region and a succeeding region of the information signal.

Claims

1. Information signal reconstructor configured to reconstruct, using aliasing cancellation, an information signal from a lapped transform representation of the information signal comprising, for each of consecutive, overlapping regions of the information signal, a transform of a windowed version of the respective region, wherein the information signal reconstructor is configured to reconstruct the information signal at a sample rate which changes at a border between a preceding region and a succeeding region of the information signal from a first sample rate within the preceding region to a second sample rate, different from the first sample rate, within the succeeding region, the information signal reconstructor comprises

a retransformer configured to apply a retransformation on the transform of the windowed version of the preceding region so as to acquire a retransform for the preceding region, and apply a retransformation on the transform of the windowed version of the succeeding region so as to acquire a retransform for the succeeding region, wherein the retransform for the preceding region and the retransform for the succeeding region overlap at an aliasing cancellation portion at the border between the preceding and succeeding regions;

a resampler configured to resample, by interpolation, the retransform for preceding region and/or the retransform for the succeeding region at the aliasing cancellation portion according to a sample rate change at the border; and

a combiner configured to perform aliasing cancellation between the retransforms for the preceding and succeeding regions as acquired by the resampling at the aliasing cancellation portion so as to reconstruct the information signal in a form sampled at the first sample rate within a portion of the retransform for the preceding region, preceding the aliasing cancellation portion, and sampled at the second sample rate within a portion of the retransform for the succeeding region, succeeding the aliasing cancellation portion.

2. Information signal reconstructor according to claim 1, wherein the resampler is configured to resample the retransform for the preceding region at the aliasing cancellation portion according to the sample rate change at the border.

3. Information signal reconstructor according to claim 1, wherein a ratio of a transform length of the retransformation applied to the transform of the windowed version of the preceding region to a temporal length of the preceding region differs from a ratio of a transform length of the retransformation applied to the windowed version of the succeeding region to a temporal length of the succeeding region by a factor corresponding to the sample rate change.

4. Information signal reconstructor according to claim 3, wherein the temporal lengths of the preceding and succeeding regions are equal to each other, and the retransformer is configured to restrict the application of the retransformation on the transform of the windowed version of the preceding region to a low-frequency portion of the transform of the windowed version of the preceding region and/or restrict the application of the retransformation on the transform of the windowed version of the succeeding region on a low-frequency portion of the transform of the windowed version of the succeeding region.

5. Information signal reconstructor according to claim 1, wherein a transform length of the transform of the windowed version of the regions of the information signal and a temporal length of the regions of the information signal are constant, and the information signal reconstructor is configured to locate the border responsive to a control signal.

8. Information signal reconstructor according to claim 1, wherein the transform length of the transform of the windowed version of the regions of the information signal varies, while a temporal length of the regions of the information signal is constant, wherein the information signal reconstructor is configured to locate the border by detecting a change in the transform length of the windowed version of the regions of the information signal.

9. Information signal reconstructor according to claim 8, wherein the retransformer is configured to adapt a transform length of the retransformation applied on the transform of the windowed version of the preceding and succeeding regions to the transform length of the transform of the windowed version of the preceding and succeeding regions.

11. Information signal reconstructor according to claim 1, wherein the lapped transform is critically sampled such as an MDCT.

12. Information signal reconstructor according to claim 1, wherein the lapped transform representation is a complex valued filterbank.

13. Information signal reconstructor according to claim 1, wherein resampler is configured to use a linear or spline interpolation for the interpolation.

14. Information signal reconstructor according to claim 1, wherein the sample rate decreases at the border and the retransformer is configured to, in applying the retransformation on the transform of the windowed version of the preceding region, attenuate, or set to zero, higher frequencies of the transform of the windowed version of the preceding region.

24. Information signal reconstructor according to claim 1, wherein the combiner is configured to perform the aliasing cancellation between the retransforms for the preceding and succeeding regions as acquired by the resampling at the aliasing cancellation portion by arranging the retransforms for the preceding and succeeding regions so as to overlap within the aliasing cancellation portion and adding, for each temporal sample position of the information signal, either

a resampled version of the retransform for the preceding region, as acquired by the resampling at the aliasing cancellation portion, with a not-resampled version of the retransform for the succeeding region, or

a resampled version of the retransform for the succeeding region, as acquired by the resampling at the aliasing cancellation portion, with a not-resampled version of the retransform for the preceding region.

6. Resampler composed of a concatenation of a filterbank for providing a lapped transform representation of an information signal, and an inverse filterbank comprising an information signal reconstructor configured to reconstruct, using aliasing cancellation, the information signal from the lapped transform representation of the information signal, wherein the lapped transform representation of the information signal comprises, for each of consecutive, overlapping regions of the information signal, a transform of a windowed version of the respective region, wherein the information signal reconstructor is configured to reconstruct the information signal at a sample rate which changes at a border between a preceding region and a succeeding region of the information signal from a first sample rate within the preceding region to a second sample rate, different from the first sample rate, within the succeeding region, the information signal reconstructor comprises

a retransformer configured to apply a retransformation on the transform of the windowed version of the preceding region so as to acquire a retransform for the preceding region, and apply a retransformation on the transform of the windowed version of the succeeding region so as to acquire a retransform for the succeeding region, wherein the retransform for the preceding region and the retransform for the succeeding region overlap at an aliasing cancellation portion at the border between the preceding and succeeding regions;

a resampler configured to resample, by interpolation, the retransform for the preceding region and/or the retransform for the succeeding region at the aliasing cancellation portion according to a sample rate change at the border; and

a combiner configured to perform aliasing cancellation between the retransforms for the preceding and succeeding regions as acquired by the resampling at the aliasing cancellation portion so as to reconstruct the information signal in a form sampled at the first sample rate within a portion of the retransform for the preceding region, preceding the aliasing cancellation portion, and sampled at the second sample rate within a portion of the retransform for the succeeding region, succeeding the aliasing cancellation portion,

wherein a transform length of the transform of the windowed version of the regions of the information signal and a temporal length of the regions of the information signal are constant, and the information signal reconstructor is configured to locate the border responsive to a control signal.

7. Information signal encoder comprising a resampler composed of a concatenation of a filterbank for providing a lapped transform representation of an information signal, and an inverse filterbank comprising an information signal reconstructor configured to reconstruct, using aliasing cancellation, the information signal from the lapped transform representation of the information signal, the lapped transform representation of the information signal comprises, for each of consecutive, overlapping regions of the information signal, a transform of a windowed version of the respective region, wherein the information signal reconstructor is configured to reconstruct the information signal at a sample rate which changes at a border between a preceding region and a succeeding region of the information signal from a first sample rate within the preceding region to a second sample rate, different from the first sample rate, within the succeeding region, the information signal reconstructor comprises

a retransformer configured to apply a retransformation on the transform of the windowed version of the preceding region so as to acquire a retransform for the preceding region, and apply a retransformation on the transform of the windowed version of the succeeding region so as to acquire a retransform for the succeeding region, wherein the retransform for the preceding region and the retransform for the succeeding region overlap at an aliasing cancellation portion at the border between the preceding and succeeding regions;

a resampler configured to resample, by interpolation, the retransform for preceding region and/or the retransform for the succeeding region at the aliasing cancellation portion according to a sample rate change at the border; and

a combiner configured to perform aliasing cancellation between the retransforms for the preceding and succeeding regions as acquired by the resampling at the aliasing cancellation portion so as to reconstruct the information signal in a form sampled at the first sample rate within a portion of the retransform for the preceding region, preceding the aliasing cancellation portion, and sampled at the second sample rate within a portion of the retransform for the succeeding region, succeeding the aliasing cancellation portion,

wherein a transform length of the transform of the windowed version of the regions of the information signal and a temporal length of the regions of the information signal are constant, and the information signal reconstructor is configured to locate the border responsive to a control signal,

and a compression stage configured to compress the reconstructed information signal, the information signal encoder further comprising a sample rate control configured to control the control signal depending on an external information on available transmission bitrate.

10. Information signal reconstructor comprising a decompressor configured to reconstruct a lapped transform representation of an information signal from a data stream, and an information signal reconstructor configured to reconstruct, using aliasing cancellation, an information signal from a lapped transform representation of the information signal comprising, for each of consecutive, overlapping regions of the information signal, a transform of a windowed version of the respective region, wherein the information signal reconstructor is configured to reconstruct the information signal at a sample rate which changes at a border between a preceding region and a succeeding region of the information signal from a first sample rate within the preceding region to a second sample rate, different from the first sample rate, within the succeeding region, the information signal reconstructor comprises

a retransformer configured to apply a retransformation on the transform of the windowed version of the preceding region so as to acquire a retransform for the preceding region, and apply a retransformation on the transform of the windowed version of the succeeding region so as to acquire a retransform for the succeeding region, wherein the retransform for the preceding region and the retransform for the succeeding region overlap at an aliasing cancellation portion at the border between the preceding and succeeding regions;

a resampler configured to resample, by interpolation, the retransform for preceding region and/or the retransform for the succeeding region at the aliasing cancellation portion according to a sample rate change at the border; and

a combiner configured to perform aliasing cancellation between the retransforms for the preceding and succeeding regions as acquired by the resampling at the aliasing cancellation portion so as to reconstruct the information signal in a form sampled at the first sample rate within a portion of the retransform for the preceding region, preceding the aliasing cancellation portion, and sampled at the second sample rate within a portion of the retransform for the succeeding region, succeeding the aliasing cancellation portion,

wherein the transform length of the transform of the windowed version of the regions of the information signal varies, while a temporal length of the regions of the information signal is constant, wherein the information signal reconstructor is configured to locate the border by detecting a change in the transform length of the windowed version of the regions of the information signal,

wherein the retransformer is configured to adapt a transform length of the retransformation applied on the transform of the windowed version of the preceding and succeeding regions to the transform length of the transform of the windowed version of the preceding and succeeding regions,

configured to reconstruct, using aliasing cancellation, the information signal from the lapped transform representation.

15. Information signal transformer configured to generate a lapped transform representation of an information signal using an aliasing-causing lapped transform, comprising

an input for receiving the information signal in the form of a sequence of samples;

a grabber configured to grab consecutive, overlapping regions of the information signal;

a resampler configured to apply, by interpolation, a resampling onto at least a subset of the consecutive, overlapping regions of the information signals the resampling resulting in each of the consecutive, overlapping portions comprising a respective constant sample rate, with the respective constant sample rate varying among the consecutive, overlapping regions;

a windower configured to apply a windowing on the consecutive, overlapping regions of the information signal; and

a transformer configured to individually apply a transform on the windowed regions.

16. Information signal transformer according to claim 15, wherein the grabber is configured to perform the grabbing of the consecutive, overlapping regions of the information signal such that the consecutive, overlapping regions of the information signal are of constant time length.

17. Information signal transformer according to claim 15, wherein the grabber is configured to perform the grabbing of the consecutive, overlapping regions of the information signal such that the consecutive, overlapping regions of the information signal comprise a constant time offset.

18. Information signal transformer according to claim 16, wherein the sequence of samples comprises a varying sample rate switching from a first sample rate to a second sample rate at a predetermined time instant, wherein the resampler is configured to apply the resampling onto the consecutive, overlapping regions overlapping with the predetermined time instant so that the constant sample rate thereof switches merely once from the first sample rate to the second sample rate.

19. Information signal transformer according to claim 18, wherein the transformer is configured to adapt a transform length of the transform of each windowed region to a number of samples of the respective windowed region.

20. Method for reconstructing, using aliasing cancellation, an information signal from a lapped transform representation of the information signal comprising, for each of consecutive, overlapping regions of the information signal, a transform of a windowed version of the respective region, wherein the information signal reconstructor is configured to reconstruct the information signal at a sample rate which changes at a border between a preceding region and a succeeding region of the information signal from a first sample rate within the preceding region to a second sample rate, different from the first sample rate, within the succeeding region, the method comprising

applying a retransformation on the transform of the windowed version of the preceding region so as to acquire a retransform for the preceding region, and apply a retransformation on the transform of the windowed version of the succeeding region so as to acquire a retransform for the succeeding region, wherein the retransform for the preceding region and the retransform for the succeeding region overlap at an aliasing cancellation portion at the border between the preceding and succeeding regions;

resampling, by interpolation, the retransform for preceding region and/or the retransform for the succeeding region at the aliasing cancellation portion according to a sample rate change at the border; and

performing aliasing cancellation between the retransforms for the preceding and succeeding regions as acquired by the resampling at the aliasing cancellation portion so as to reconstruct the information signal in a form sampled at the first sample rate within a portion of the retransform for the preceding region, preceding the aliasing cancellation portion, and sampled at the second sample rate within a portion of the retransform for the succeeding region, succeeding the aliasing cancellation portion.

21. Method for generating a lapped transform representation of an information signal using an aliasing-causing lapped transform, comprising

receiving the information signal in the form of a sequence of samples;

grabbing consecutive, overlapping regions of the information signal;

applying, by interpolation, a resampling onto at least a subset of the consecutive, overlapping regions of the information signals the resampling resulting in each of the consecutive, overlapping portions comprising a respective constant sample rate, with the respective constant sample rate varying among the consecutive, overlapping regions;

applying a windowing on the consecutive, overlapping regions of the information signal; and

individually applying a transformation on the windowed regions.

22. Non-transitory computer-readable medium having stored thereon a computer program comprising a program code for performing, when running on a computer, a method for reconstructing, using aliasing cancellation, an information signal from a lapped transform representation of the information signal comprising, for each of consecutive, overlapping regions of the information signal, a transform of a windowed version of the respective region, wherein the information signal reconstructor is configured to reconstruct the information signal at a sample rate which changes at a border between a preceding region and a succeeding region of the information signal from a first sample rate within the preceding region to a second sample rate, different from the first sample rate, within the succeeding region, the method comprising

applying a retransformation on the transform of the windowed version of the preceding region so as to acquire a retransform for the preceding region, and apply a retransformation on the transform of the windowed version of the succeeding region so as to acquire a retransform for the succeeding region, wherein the retransform for the preceding region and the retransform for the succeeding region overlap at an aliasing cancellation portion at the border between the preceding and succeeding regions;

resampling, by interpolation, the retransform for preceding region and/or the retransform for the succeeding region at the aliasing cancellation portion according to a sample rate change at the border; and

performing aliasing cancellation between the retransforms for the preceding and succeeding regions as acquired by the resampling at the aliasing cancellation portion so as to reconstruct the information signal in a form sampled at the first sample rate within a portion of the retransform for the preceding region, preceding the aliasing cancellation portion, and sampled at the second sample rate within a portion of the retransform for the succeeding region, succeeding the aliasing cancellation portion.

23. Non-transitory computer-readable medium having stored thereon a computer program comprising a program code for performing, when running on a computer, a method for generating a lapped transform representation of an information signal using an aliasing-causing lapped transform, comprising

receiving the information signal in the form of a sequence of samples;

grabbing consecutive, overlapping regions of the information signal;

applying, by interpolation, a resampling onto at least a subset of the consecutive, overlapping regions of the information signals the resampling resulting in each of the consecutive, overlapping portions comprising a respective constant sample rate, with the respective constant sample rate varying among the consecutive, overlapping regions;

applying a windowing on the consecutive, overlapping regions of the information signal; and

individually applying a transformation on the windowed regions.